Multiscale strength (MS) models: their foundation, their successes, and their challenges

Multiscale strength (MS) models are constructed to capture a natural hierarchy in the deformation of metals such as V and Ta starting with atomic bonding and extending up through the mobility of individual dislocations, the evolution of dislocation networks and so on until the ultimate material response at the scale of an experiment. In practice, the hierarchy is described by quantum mechanics, molecular dynamics, dislocation dynamics, and so on, ultimately parameterizing a continuum constitutive model. We review the basic models and describe how they operate at extremely high pressures and strain rates, such as in Rayleigh-Taylor plastic flow experiments. The models use dislocation density as a state variable, and describe time-dependent, as well as rate-dependent, plasticity. They make interesting and testable predictions about transients in plastic flow. There are also clear challenges, however. The current MS models do not include a variety of mechanisms known to be important at low rates. Still, MS models provide compelling insight into plastic deformation of metals under extreme pressures and strain rates.